Dissertation Defense Schedule
Academic Excellence
Sharing original dissertation research is a principle to which the University of Delaware is deeply committed. It is the single most important assignment our graduate students undertake and upon completion is met with great pride.
We invite you to celebrate this milestone by attending their dissertation defense. Please review the upcoming dissertation defense schedule below and join us!
PROGRAM | Electrical & Computer Engineering
Investigation into the Stability of Silicon Heterojunction Solar Cells and the Metastability of Cadmium Telluride Solar Cells
By: Gbenga Daniel Obikoya Chair: Steven Hegedus
ABSTRACT
Solar cell technologies are presently undergoing evolutionary changes in design and fabrication to further improve the power conversion efficiency at a reduced fabrication cost. However, there is no guarantee that the new cell performance will not be compromised under actual outdoor field conditions, thus necessitating the need to investigate reliability issues in solar cells using accelerated indoor exposure and testing methods.
In the first part of this work, silicon heterojunction (SHJ) solar cells were exposed to accelerated life testing to investigate the effect of varying cell structure and the effect of varying exposure conditions on the degradation mechanism of the SHJ cells. The cell structural variation (by eliminating rear-side indium layer) caused a degradation in the open-circuit voltage due to loss of passivation for exposure at 90°C. Increasing the accelerated testing temperature from 90°C to 120°C in standard SHJ cells (with the rear side indium layer) caused a significant degradation in fill factor because of increase in series resistance and collection barrier. Therefore, an attempt to reduce the fabrication cost by eliminating the rear indium layer on SHJ cells will significantly compromise their long-term reliability and standard SHJ modules deployed in very hot climates may see increased degradation over long periods of time.
In the 2nd part of this work, the effect of doping and metastable defects on the performance of cadmium telluride (CdTe) solar cells were investigated. Incorporation of antimony dopant into CdTe solar cells improves their performance compared to the copper-doped cells due to higher carrier lifetime, better interface quality and partly due to doping density achieved. Additionally, when CdTe cells were exposed to light soaking at 1 sun for 50 hours, low efficiency arsenic-doped cells showed the highest improvement in open-circuit voltage and fill factor compared to antimony and copper-doped cells having higher initial efficiency. We show that the arsenic-doped cells improved significantly under light soaking after the metastable defects were passivated with excess photogenerated carriers. However, when stored in the dark for 50 hours, the efficiency returned to its initial poor value thus confirming that this is a metastable defect. Considering this instability, it is crucial to keep improving on the standard measurement and pre-testing light exposure procedures to investigate the origin of metastable defects and to mitigate them, as the CdTe solar cell technology evolves.
The Process
Step-by-Step
Visit our “Step-by-Step Graduation Guide” to take you through the graduation process.From formatting your Dissertation to Doctoral Hooding procedures.
Dissertation Manual
Wondering how to set up the format for your paper. Refer to the “UD Thesis/Dissertation Manual” for formatting requirements and more.
Defense Submission Form
This form must be completed two weeks in advance of a dissertation defense to meet the University of Delaware Graduate and Professional Education’s requirements.
